Recording Guitars: Miking Acoustics, Part 2

Last installment we examined a few basic one-mic techniques for recording acoustic guitar. This week, let’s investigate some more involved multi-mic techniques. As with recording guitar amps, you can often achieve a broader, more multi-dimensional sound from an acoustic by carefully positioning more than one microphone.

Be aware, however, that two mics are not always better than one: in some cases you might want the straightforward, less harmonically saturated (less “frequency range-dominating,” if you will) sound of just a single microphone, when you want to have a driving acoustic rhythm guitar part in a busy mix where other sounds are more prominent, for example. With that in mind, if you want to coax the richest, deepest, most “in-the-room” acoustic guitar sounds onto your recording, you will often turn to two mics to do it. Here are some techniques to try out:

Spaced Stereo Pair: This sounds pretty obvious, but there are some pretty huge variables depending upon what tones your acoustic guitar generates from different vantage points, sonically speaking (refer to Miking Acoustics Part 1 for more detail on this). Basically, for this technique you use two of the same mics (or at least very similar, if that’s all you’ve got) positioned about a foot back from the guitar, and three feet apart. Placing them in this three-to-one relationship, ie three times as far from each other as they are from the sound source, helps to minimize phase cancellation between the mics. This technique can yield a broad and fairly realistic stereo image, although it can sometimes result in the feeling of there being a “hole in the middle” of the sonic picture, depending how wide you pan them in the mix. Our next technique seeks to eliminate that …

XY Pair: Also called Coincident Pair, this technique involves placing two identical microphones—usually cardiod mics—with their capsules (their sound-receiving ends) as close together as possible without touching, but at right angles, so that the mic on the left is aiming across toward the right of the sound source, and the right microphone is aiming toward the left side of the sound source. As such, the mics are positioned in a “Y” pattern (with the base of the “Y” pointing toward the sound source), and capturing a sound source that crosses over to them in an “X” pattern. This might seem an odd configuration, but it can be very effective at creating a realistic stereo image that has no “hole” in the middle.

Mid-Side Pair: This is an interesting technique that can yield a broad, full stereo image. It requires either two microphones with figure-eight patterns (that is, which receive sound equally from in front or behind their capsules), or one figure-eight and one cardioid, along with some know-how regarding how you record and/or mix the signals. Although it uses two microphones, the M-S Pair technique results in three signals, two from the figure-eight side mic, split far left and far right, with one reverse-phase of the other to create a perfect stereo image, and one from the mid mic, placed center to “fill in the hole” without any phase cancellation. Place the figure-eight mic (or one of two) side-on to a sonically desirable point on the acoustic guitar, a slight distance away. Place the second, or the cardioid mic, with the capsule as close to the first (side) mic as you can get it, without touching, and aiming straight at the sound source. Now, this technique requires more than just positioning, so here’s what you do next:

If you are recording into a digital audio workstation (DAW) that has an M-S Decoder insert, which many do, simply record the side mic to one side of a stereo channel and the mid mic to the other. Bring up your decoder insert, and it will split the figure-eight mic L-R, reversing the phase of one, and place your mid mic center. Boom—big stereo image. If you’re recording the old fashioned way, split the signal of your mid mic to two channels on your mixer or mic preamp, reverse the phase of one, and patch these two to your recording device, later to be panned L-R in the mix. Record the mid mic straight to one channel, and position it in the middle. Note that you can adjust the width of the stereo field by bringing the L-R channels further toward or away from center, but if you bring them entirely to center their signals disappear completely, because the reverse-phase images cancel either other out. The mid mic sound remains, however. It’s a fascinating and rather complex sonic phenomenon, and one worth exploring.

Dual Mono Pair: Strictly speaking, a true stereo image should capture identical left and right images of a sound source, as the above techniques do. If you use two different mics, and or place two mics in very different and unequal positions around the sound source, you aren’t really recording in stereo, but in dual mono. Which is not to rule out such a technique at all, because doing so can often yield great results. Consider that an acoustic guitar produces very different tones from different parts of its body and neck anyway, as discussed last time, and it’s clear that you might get some interesting results from placing different mics at different points around the guitar and either blending them entirely together in mono, or positioning them L-R to some degree across the field. Look back at the single-mic positions I discussed in Miking Acoustics Part 1 and consider that you can use a combination of any two of these. Even when used in “pseudo stereo”—that is, two differently recorded points of the guitar panned in stereo—you can often yield a big and sonically pleasing sound from this technique. Of course you need to be aware of phase cancellation issues with such techniques, and do what you can to minimize them.

Corner Loading: This one was passed along to me by my recording-engineer friend Huw Price, who is also the author of Recording Guitar & Bass (Backbeat Books), which carries a wealth of information on these subjects, rendered in greater detail than we have space for here. A reflective corner—you’ll find plenty in your own house, apartment or studio—naturally emphasizes the low frequencies of any sound played into it. Sit with your guitar aiming into such a corner, and place two identical or similar mics, one either side of your (or the guitarist’s) head, also aiming into the corner. Play, record, and check out the full, rich sound it captures. You can also use this technique with just one mic for a fat-bottomed mono recording.

Try these out and discover which might work for you. Tweak them, experiment, invent your own radical—or super-simple—mic techniques. Whatever works, works.

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